COPD is a costly disease with a large burden of costs driven by healthcare utilization during acute exacerbations of illness, particularly those driven by emergency room and hospital visits. Additionally, a large proportion of individuals with COPD recently hospitalized for acute exacerbations are re-hospitalized both within one month but also within a year. These re-hospitalizations place a tremendous burden of cost on society not just due to direct costs but also indirect costs and lost productivity. A majority of individuals with COPD are discharged home, back to the very environment that was likely contributing to their disease morbidity. Indoor air pollution and allergen sensitization with exposure are important components of the home environment that likely contribute to exacerbation risk as has been shown in mostly stable, outpatient populations of former smokers with COPD. However, little is known about these factors in the highly vulnerable population of individuals recently hospitalized with COPD exacerbations, who have different characteristics and competing risks than stable outpatient populations. Accordingly, we propose a single center observational study of individuals with COPD, to be recruited during hospitalization for COPD exacerbation. We hypothesize that in-home air pollution, including ultrafine and fine particulate matter and nitrogen dioxide (Specific Aim 1) as well as allergen sensitization with exposure (Specific Aim 2) will be associated with heightened risk for the primary outcome of interest, re-hospitalization for COPD exacerbation. The home environment will be assessed within 1 week of discharge from the hospital, and again at 3, 6, and 9 months post index hospitalization in addition to clinical measures. Outcomes will be assessed up to one year post index hospitalization. This study will provide much needed information about the contribution of indoor air pollution and allergen sensitization with exposure to re- hospitalizations in the high-risk population of individuals with COPD recently hospitalized for exacerbation. We believe that this study can provide valuable information which can ultimately be utilized to design interventions to modify the home environment post-hospital discharge with the goal to improve outcomes including re- hospitalization risk in COPD. 1